This invention relates to vehicle air system, and more specifically to a commercial vehicle air system having a dryer apparatus.
Commercial vehicles such as trucks, buses, and large commercial vehicles are typically equipped with a compressed air system in which the brakes of the vehicle are actuated by compressed air. An air compressor is often operated by the vehicle engine and generates pressurized air for the operation of air brakes and other devices that rely on pneumatic air. However, the operation of an air compressor inherently raises the temperature of the air and also produces contaminants such as oil. The accumulation of water, oil and other contaminants present problems that can adversely affect the operation of the brake system and other devices that rely on the compressed air. More specifically, moisture entrained in the air brake system may during cold weather operation cause the components of the air brake system to freeze, thus rendering the system inoperable.
Vehicle air systems typically include a filter and an air dryer to remove coalesced oil, oil vapor and water vapor of the compressed air. If the dryer is a desiccant dryer, for example, a problem can exist in that once the desiccant is saturated with contamination the dryer ceases to perform the function of providing dry air. It is difficult to know whether the desiccant needs to be replaced, and air dryers can be difficult to service because lines must be disconnected in order to remove the desiccant or desiccant canister. An operator may have to drain air reservoir tanks or perform other mechanical procedures to determine the quality of the air in the system.
Some vehicle air systems further include indicating devices downstream from the dryer to indicate excessive moisture present in the compressed air system. However, there can often be temporary conditions such as excessive demand on the dryer that can affect the quality of the air through the system and therefore yield a false signal with regard to the desiccant. Therefore, a need exists for an air system that addresses the ability to monitor the effectiveness of the desiccant in the dryer.